The ship propulsion device disclosed in Patent Literature 1 is conventionally known as a ship propulsion device for propelling a ship. FIG. 10 schematically illustrates the construction of a known ship propulsion device. As shown in FIG. 10, the ship propulsion device 100 comprises a propeller 101 for propelling a ship, an engine 102 for rotating the propeller 101, and a reduction/reversing gear 103 that is capable of transmitting the revolutions of the engine 102 to the propeller 101. The reduction/reversing gear 103 is provided with a clutch (not shown) inside. The ship propulsion device 100 comprises an input device 104 that is capable of inputting value that indicates the state of the clutch inside the reduction/reversing gear 103, and a control device 105 that controls the state of the clutch and the operation of the engine 102.
When a ship is propelled using a ship propulsion device 100 having such a structure, as a first step, with the clutch mounted in the reduction/reversing gear 103 disengaged, the control device 105 allows the engine 102 to start when a switch (not shown) is turned on. Next, while the engine 102 is operating, the control device 105 puts the clutch in the reduction/reversing gear 103 into a partially engaged state based on input of the input device 104. This allows the revolutions of the engine 102 to be transmitted to the propeller 101 through the clutch in the reduction/reversing gear 103, causing the propeller 101 to start rotating. Thereafter, with the engine 102 operating and the clutch in a partially engaged state, the control device 105 puts the clutch into an engaged state based on input of the input device 104. This completely connects the clutch, so that the revolutions of the engine 102 are fully transmitted to the propeller 101 through the clutch. As a result, the propeller 101 fully rotates. Thus, by bringing the clutch in the reduction/reversing gear 103 from a disengaged state to an engaged state via a partially engaged state, the propeller 101 can be rotated, thereby propelling the ship.